The present invention relates to a leadframe, which includes leads with land electrodes functioning as external terminals and can replace a conventional leadframe with beam-like leads. The present invention also relates to a method for manufacturing a land-grid-array (LGA) resin-molded semiconductor device, in which a semiconductor chip is bonded onto the leadframe and the assembly is molded with a resin encapsulant.
In recent years, to catch up with rapidly advancing downsizing of electronic units, it has become increasingly necessary to assemble semiconductor components, like resin-molded semiconductor devices, at a higher and higher density. In response, sizes and thicknesses of semiconductor components have also been noticeably reduced. In parallel with this downsizing trend, the number of pins needed for a single electronic unit is also increasing day after day. To meet these demands, resin-molded semiconductor devices of a greatly shrunken size and with a drastically reduced thickness should now be assembled at an even higher density.
Hereinafter, a conventional leadframe for a resin-molded semiconductor device will be described.
FIG. 22 is a plan view illustrating the structure of a conventional leadframe. As illustrated in FIG. 22, the leadframe includes rectangular die pad 102, support leads 103, beam-like inner leads 104, outer leads 105 and tie bars 106, all of these members being provided inside a frame rail 101. The die pad 102 is used for mounting a semiconductor chip thereon. The support leads 103 support the die pad 102. The inner leads 104 will be electrically connected to the semiconductor chip with some connection members like metal fine wires. The outer leads 105 are joined to the respective inner leads 104 and to be connected to external terminals. And the tie bars 106 are provided for joining and fixing the outer leads 105 together and for preventing a resin encapsulant from overflowing during a resin molding process.
It should be noted that normally the leadframe does not consist of the single pattern shown in FIG. 22, but is made up of a plurality of such patterns, which are arranged and connected together both horizontally and vertically.
Next, a known resin-molded semiconductor device will be described. FIG. 23 is a cross-sectional view illustrating a resin-molded semiconductor device including the leadframe shown in FIG. 22.
As shown in FIG. 23, a semiconductor chip 107 has been bonded onto the die pad 102 of the leadframe and electrically connected to the inner leads 104 with metal fine wires 108. The semiconductor chip 107 on the die pad 102, the inner leads 104 and so on have been molded with a resin encapsulant 109. The outer leads 105 protrude from the side faces of the resin encapsulant 109 and have had their outer ends bent downward.
Next, a method for manufacturing the resin-molded semiconductor device will be described with reference to FIGS. 23 and 24. First, the semiconductor chip 107 is bonded, with an adhesive, onto the die pad 102 of the leadframe. This process step is called “die bonding”. Next, the semiconductor chip 107 is connected to the respective inner ends of the inner leads 104 with the metal fine wires 108. This process step is called “wire bonding”. Subsequently, the semiconductor chip 107 and a portion of the leadframe inside the tie bars 106 (i.e., the inner leads 104 and so on) are molded with the resin encapsulant 109 such that the outer leads 105 protrude outward. This process step is called “resin molding”. Finally, the tie bars 106 are cut off at the boundary between the tie bars 106 and the resin encapsulant 109 to separate the outer leads 105 from each other and remove the frame rail 101, and the respective outer ends of the outer leads 105 are bent. This process step is called “tie bar cutting and bending”. In this manner, a resin-molded semiconductor device with the structure shown in FIG. 23 is completed. In FIG. 24, the dashed line indicates a region where the assembly is molded with the resin encapsulant 109.
As described above, the number of devices that should be integrated within a single semiconductor chip, or the number of pins per chip, has been on the rise these days. Thus, the number of outer leads should also be increased to catch up with this latest trend. That is to say, the number of inner leads, which are joined to the outer leads, should preferably be increased to cope with such an implementation. However, the width of the inner (or outer) lead has a processable limit. Thus, as the number of inner (or outer) leads is increased, the overall size of the leadframe and that of the resulting resin-molded semiconductor device also increase. In view of these states in the art, it is difficult to realize a downsized and thinned resin-molded semiconductor device. On the other hand, if only the number of inner leads is increased to cope with the rise in the number of pins needed for a semiconductor chip while using a leadframe of substantially the same size, then the width of a single inner lead should be further reduced. In such a case, however, it is much more difficult to perform various process steps for forming the leadframe, like etching, as originally designed.
Recently, face-bonded semiconductor devices, such as ball grid array (BGA) types and land grid array (LGA) types, are also available. In the semiconductor device of any of these types, first, a semiconductor chip is mounted onto a carrier (e.g., a printed wiring board) including external electrodes (e.g., ball electrodes or land electrodes) on its bottom. Next, the semiconductor chip is electrically connected to the external electrodes. And then the chip and its associated members are molded with a resin encapsulant on the upper surface of the carrier. The semiconductor device of this face-bonded type, which is mounted directly on a motherboard on the bottom, will be a mainstream product in the near future. Accordingly, it is now clear that the conventional leadframe and resin-molded semiconductor device using the leadframe will soon be out of date under the circumstances such as these.
Also, the conventional resin-molded semiconductor device includes outer leads protruding outward from the side faces of a resin encapsulant, and is supposed to be mounted onto a motherboard by bonding the outer leads to the electrodes on the motherboard. Accordingly, the conventional device cannot be mounted onto the board so reliably as the semiconductor devices of the BGA and LGA types. Nevertheless, the semiconductor devices of the BGA and LGA types are expensive, because these devices use a printed wiring board.